The present invention relates to a method and apparatus for detecting charged particles in an aqueous solution, in which electrodes are immersed by supplying a stepping potential and measuring the induced impulse current. Most studies on electrodes in the past were made during steady state, such as the measurement of the H+ and other ions, or the electrical signal measurement. These studies focused on ways to eliminate the transient response to the electrodes for EKG (electrocardiogram) or EEG (electro-encephalogram), which depends on the ingredient of the surrounding solution, as described in Electrode Kinetics by John Albery, Oxford University press, 1975 and Electrodes and the Measurement of Bioelectric Events by L. A. Geddes, Wiley-interscience, 1972.